136. Used but not useless: reusing CIDRs in 7 day estrous synchronization programs of beef cows.

Abstract The controlled internal drug release (CIDR) represents 85% of the cost in estrous synchronization protocols for beef cattle, which are adopted only by 7% of beef ranchers. Reusing CIDRs can reduce the cost and increase the adoption of such programs. In experiment 1, we hypothesized that circulating progesterone (P4) concentrations are similar between autoclaved and chlorhexidine-disinfected devices for 7 days and remain above 1 ng/mL regardless of the number of uses, for up to four uses. In experiment 2, we hypothesized that pregnancy by artificial insemination (preg/AI) is similar among devices used up to four times in a 7-day synchronization protocol in Bos taurus cows. In experiment 1, heifers (n = 21) without a corpus luteum (CL) were assigned to the following treatments for 7 days: a new CIDR, and CIDRs previously used once (7 days), twice, or three times (CIDR-2nd, CIDR-3rd, and CIDR-4th, respectively). Devices were disinfected with chlorhexidine or by autoclaving between each use. Circulating P4 concentrations were measured daily. Autoclaving did not affect circulating P4 concentrations during the insertion period (P > 0.10). In experiment 2, beef cows (n = 1,238; 557/681 primiparous/multiparous) were submitted to a 7-day CO-Synch + CIDR protocol. On day-10 (D-10), cows were randomly assigned to the following treatments: CIDR-1st (n = 319), CIDR-2nd (n = 309), CIDR-3rd (n = 304), and CIDR-4th (n = 306), received an injection of gonadorelin, and were subjected to ovarian ultrasonography to detect presence/absence of a CL. On D-3, CIDRs were removed and timing of removal was recorded, cows received an injection of prostaglandin F2α, were fitted with an estrous patch, and were subjected to transrectal ultrasonography to measure the diameter of the largest follicle and the presence of a CL. In a subgroup (n = 342 and 910 respectively), blood samples were collected to measure circulating P4concentrations and estrus was monitored every 4-6 hours to calculate proestrus length (interval from CIDR removal to estrus onset). Cows were timed AI 60-66 hours after D-3 with the semen of 28 bulls. Pregnancy was diagnosed on D30/35. Statistical analyses were performed using mixed-effects or logistic regression on SAS. Overall, 55.87% of cows expressed estrus and preg/AI was 44.86%. The number of CIDR uses affected negatively the circulating P4 concentrations (P = 0.0041) and positively the follicular diameter on D-3 (P = 0.021), but did not affect proestrus length or estrous expression (P > 0.10). There was an interaction between CIDR treatment and parity on preg/AI (P = 0.069). In multiparous cows, pregnancy/AI did not differ among treatments (P = 0.58), whereas in primiparous cows CIDR-4th reduced preg/AI by 47.3%, 55.1%, and 49.9% compared with CIDR-1st, CIDR-2nd, and CIDR-3rd, respectively. In conclusion, for 7-day protocols, CIDRs can be reused up to 3 times (4 total uses) in multiparous cows, but only up to 2 times (3 total uses) in primiparous cows.